Method of inhibiting corrosion in oil field produced fluids

ABSTRACT

A method for treating a hydrocarbon stream containing free sulfur wherein a formulation comprising a diaryldisulfide and a film forming corrosion inhibitor are introduced into the hydrocarbon stream.

BACKGROUND OF THE INVENTION

This invention relates generally to the use of corrosion inhibitingcomposition comprising diaryldisulfide in oil and gas field producedfluids. In one aspect the invention relates to a method for inhibitingcorrosion in wells producing gas containing hydrogen sulfide.

The production of oil and natural gas from subterranean formationssometimes contains hydrogen sulfide and/or free sulfur, both of whichcontribute to corrosion of well tubulars. In addition, free sulphur candeposit and plug the well tubulars (tubing or flow lines) and otherproduction equipment. Tests have shown that corrosion is particularlysevere in areas of sulfur deposition. For example, in local regions ofthe pipe or equipment which are not capable of being scraped, the sulfurdeposits which could not be removed caused severe localized corrosion.

In order to prevent sulfur deposition, solvents are sometimes added tothe oil to dissolve the sulfur. Such solvents include amine basedsolvents and dimethyl disulfide ("DMDS").

Laboratory tests have shown that the amine based solvents are noteffective in certain applications, (e.g., in the presence of carbondioxide) and the DMDS solvents are objectionable because of their odorand toxicity. Moreover, the DMDS solvents are expensive and presentdisposal problems.

Thus, there is a need for a well treatment which inhibits both thebuildup of sulfur and the corrosion of production tubulars andequipment.

SUMMARY OF THE INVENTION

The method of the present invention involves the use of a formulation inthe treatment of wells producing oil and gas with free sulfur. Theformulation comprises a mixture of diaryldisulfides ("DADS") and a filmforming corrosion inhibitor. Both components of the formulationcontribute to the corrosion protection and the DADS also functions assolvent for the free sulfur.

Laboratory tests indicate that the combination of DADS and the filmforming corrosion inhibitor provide better protection on the metalsurface of the well tubulars than either compound alone. Although thereasons for the improved results are not fully understood, it isbelieved that the DADS may remove sulfur deposits thereby conditioningthe metal surface for deposition of the film forming corrosioninhibitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated above, the presence of free sulfur in oil and gas wellproduced fluids can create plugging and corrosion problems. Theseproblems may be particularly severe in the presence of hydrogen sulfide,carbon dioxide, and brine. If not treated with chemicals, the well canbe damaged and nonproductive.

A formulation useful in the treatment of sulfur producing oil wells andgas wells should have the following properties:

(a) good sulfur solvency

(b) good corrosion inhibition

(c) inexpensive

(d) nondamaging to equipment (non-metallic components)

(e) non-toxic

(f) easily disposable

The method of the present invention employs a corrosion inhibitorformulation containing an effective amount of DADS and a film formingcorrosion inhibitor which satisfies most of the above properties.

The method of the present invention has particular utility in thetreatment of wells producing natural gas and free sulfur because of itsdual function in dissolving the sulfur and protecting the well tubularsagainst corrosion. The term "tubulars" as used herein include both thewell tubing and the well flow line.

Each of the essential components of the formulation, as well as otherconstituents and additives, are described in detail below.

DADS: Diaryldisulfide useable in the present invention has the followinggeneral formula

    R--S--S--R'

where:

R is an alkyl group or an aromatic group; and

R' is an aromatic group.

The preferred alkyl group contains from 1 to 12 carbon atoms and can belinear or branched. The preferred aromatic group for R and R' is aphenyl or substituted phenyl group wherein the substitution is an alkylgroup containing from 1 to 3 carbon atoms.

DADS is available as a waste product generated from the caustic wash ofsour naphthas in oil refineries. DADS is a mixture of compounds havingthe R--S--S--R' formula, where R in some of the compounds is alkyl andaromatic in others. R' in the mixture of compounds includesunsubstituted and substituted phenyl groups. Most of the DADS compoundsare those wherein R and R' are different aromatic groups (e.g., phenylgroups).

DADS is commercially available from Merichem as a mixture of aryl, alkyldisulfides and diaryldisulfides, and can be produced by methods wellknown in the art.

DADS typically is a mixture of the following components:

    ______________________________________                                        COMPONENTS        RANGE (wt %)                                                ______________________________________                                        Alkyl phenyldisulfide                                                                           20-30                                                       Diphenyldisulfide 1-5                                                         Phenyltoluyldisulfide                                                                           10-15                                                       Toluylethylphenyldisulfide                                                                      10-20                                                       Diethylphenyldisulfide                                                                           5-15                                                       Naphtha            5-15                                                       ______________________________________                                    

Corrosion Inhibitor: Film forming inhibitors are a well known class ofcorrosion inhibitors and operate by forming a barrier on the welltubulars. These inhibitors consist of one or more polar groups based onN,S, or O which are attracted to the metal or metal corrosion by-productsurface. Nonpolar alkyl chains attached to the molecule are oleophilicand attract hydrocarbons to form an oily barrier on the metal surface ofthe well tubulars.

The preferred film forming inhibitors for use in the present inventionare the amine acid or salts and imidazoline derivatives.

The fatty amine corrosion inhibitors are made by combining fatty amineswith various fatty acids such as resin acids, tall oil acids, sulfurizedtall oil fatty acids, dimer and trimer acids, naphthenic acids, lauricacids, oleic acids, and the like.

The imidazolines of the following structure are particularly preferred:##STR1## where: R is an alkyl group containing from 10 to 20 carbonatoms;

R' is an alkyl group containing from 10 to 40 carbon atoms; and

Y is H, C2H4OH, or C2H4NH2

A variety of these film forming corrosion inhibitors are commerciallyavailable.

Other constitutents: The formulation may also include solvents such asaromatic solvents and surfactants such as ethoxylated alcohols orethoxylated alkyl phenols for dispersing the formulation in the producedfluids.

Formulation: The formulation will generally include the followingpackage that can be premixed:

    ______________________________________                                                 Broad     Preferred                                                                              Most                                                       Range     Range    Preferred                                                  (vol %)   (vol %)  Range                                             ______________________________________                                        DADS       60-99       75-95    75-93                                         Film Former                                                                              1-40         5-20     5-15                                         Solvent    0-30        0-5      1-5                                           Surfactant 0-20        0-5      0.5-3                                         ______________________________________                                    

Operation: Although each of the main components of the corrosioninhibitor formulation may be added separately, it is preferred topackage them in a single formulation for introduction into theproduction stream.

The formulation may be batched into the stream but preferably isintroduced continuously into the production stream at a subsurfacelocation or at the surface. A conventional "macaroni" string fed by achemical pump may be used to inject the formulation into the tubulars ata subsurface location. For surface injection, a chemical pump may beused to inject the chemical into the flow line.

The amount of the formulation actives injected will depend on theapplication. In the preferred application in produced fluids containingfree sulfur, the DADS component should be at least 4-5 times (by weight)the amount of free sulfur in the fluid treated. In most application theconcentration of the formulation in the produced fluid may range from200 to 10,000 ppm (vol), preferably 1000 to 5000 ppm. It is alsopreferred that the volume ratio of DADS to corrosion inhibitor rangesfrom 20:1 to 1:1 and preferably 10:1 to 2:1 and most preferably 7:1 to3:1.

EXPERIMENTS

Corrosivity tests were carried out in a rotating high pressure cell. Thetest equipment was as follows:

Coupons were cleaned and dipped in the treatment fluid (e.g., DADS andor corrosion inhibitor) for several minutes. The coupons then weredipped in water and placed in Autoclave Engineering stainless steelcells, each containing brine. The cells were pressurized with a chargegas to 1000 psi. The cells were placed in a wheel test cabinet at thetest conditions and exposure times. After exposure, the coupons werecleaned and weighed and the corrosion rate (mpy) for each coupondetermined.

The test materials and conditions were as follows:

    ______________________________________                                        Temperature  180 Degrees Fahrenheit                                           Brine        1000 ppm chloride + Sulfur                                       Brine        100% Brine                                                       Hydrogen Sulfide                                                                           5% of charge gas                                                 Carbon Dioxide                                                                             65% of charge gas                                                Nitrogen     30% of charge gas                                                Total Pressure                                                                             1000 psi at room temperature                                     Fluid Volume 50 cc                                                            Agitation    Rotation High Pressure Wheel Test                                Coupon Type  6" × 1/8" Rod 1018 Carbon Steel                            Run Time     24 Hours                                                         ______________________________________                                    

Additives

Corrosion Inhibitor (CI)--a fatty amine film forming corrosion inhibitor

DADS--(produced by Merichem)

Tests were carried out to ascertain the corrosion inhibition propertiesof (a) DADS alone with no elemental sulfur present and (b) DADS alone inthe presence of elemental sulfur. The test data are showing in Table I.

                  TABLE I                                                         ______________________________________                                        EXP    DADS CONC.    SULFUR    CORROSION                                      NO.    (PPM)         (WPPM)    RATE (MPY)                                     ______________________________________                                        1        0           400       225.3                                          2      1000          400       42.2                                           3      2000          400       25.8                                           4      5000          400       15.5                                           5        0           NONE      122.8                                          6      1000          NONE      145.7                                          7      2000          NONE      12.5                                           8      5000          NONE      4.7                                            ______________________________________                                    

These tests demonstrate unequivocally that DADS possess corrosioninhibition properties independent of its sulfur dissolution effects oncorrosivity.

Additional tests were conducted to determine the corrosion protectionobtained in the presence of both DADS and a film forming corrosioninhibitor. The environment contained 400 ppm sulfur.

                  TABLE II                                                        ______________________________________                                        EXP    CI CONC.     DADS      CORROSION                                       NO.    (PPM)        (PPM)     RATE (MPY)                                      ______________________________________                                         9       0            0       196.0                                           10     1000           0       23.2                                            11     2000           0       19.1                                            12       0          5000      11.3                                            13     1000         5000      10.6                                            14     2000         5000       8.2                                            15       0          7000      --                                              ______________________________________                                    

The combination of the corrosion inhibitor and DADS provided the mostprotection. Note that Experiment No. 13 gave almost twice the protectionof Experiment No. 11 at half the CI concentration. Since DADS costs farless than the commercial corrosion inhibition currently used inproduction operations, the combination of the CI and DADS is very costeffective.

Additional tests were conducted to determine the effects on corrosion byvarying the relative amounts of the DADS and the film forming corrosioninhibitor (CI). The data obtained from these test are presented in TableIII.

                  TABLE III                                                       ______________________________________                                        EXP    CI CONC.     DADS     CORROSION                                        NO.    (PPM)        (PPM)    RATE (MPY)                                       ______________________________________                                         16*     0            0      196.0                                            17       0          7000     12.5                                             18     1000         6000     6.9                                              19     2000         5000     6.3                                              20     3000         4000     6.1                                              21     4000         3000     6.6                                              22     5000         2000     7.0                                              23     6000         1000     8.2                                              24     7000           0      9.6                                              ______________________________________                                         *The blank (Experiment No. 16) was determined in Experiment No. 9.       

The above data demonstrate the synergistic effect of the combination ofthe film forming corrosion inhibitor and DADS on corrosion. Thecorrosion rate in the presence of both the CI and DADS is lower thanthat in the presence of each component alone. Note Experiment 19 at aDADS/CI volume ratio of 6:1 was lower than the CI at the same totalconcentration (7000 ppm).

What is claimed is:
 1. A method of inhibiting the corrosion in the metaltubulars of a well producing oil or gas which contains corrosive amountsof hydrogen sulfide and free sulfur, said method comprises introducinginto the produced oil or gas stream from 200 ppm to 10,000 ppm (vol) ofa formulation comprising:(a) a diaryldisulfide having the followingformula:

    R--S--S--R'

Where:R is an alkyl group or an aromatic group; and R' is an aromaticgroup; and (b) a film forming amine-based corrosion inhibitor havingpolar groups capable of attaching to the surface of the tubulars; thevolume ratio of (a)/(b) being between 2:1 and 10:1.
 2. The method ofclaim 1 wherein R is an aromatic group.
 3. The method of claim 1 whereinthe diaryldisulfide is a mixture of alkylaryl disulfides anddiaryldisulfides.
 4. The method of claim 1 wherein said volume ratio isbetween 3:1 and 7:1.
 5. The method of claim 1 wherein the film formingcorrosion inhibitor is an imidazoline corrosion inhibitor.
 6. The methodof claim 1 wherein the concentration of the formulation in the producedfluids is between 1000 to 5000 ppm by volume.
 7. The method of claim 1wherein the formulation also includes a surfactant selected from thegroup consisting of ethoxylated alcohols and ethoxylated alkyl phenolsfor dispersing the formulation in the produced oil or gas stream.